Possibly, depending on the written communication. At issue is what DM's purpose in ordering the incinerator was, and not what SS thought or supposed or was told DM's purpose was, especially relayed via a third party.
If the Crown wants to introduce evidence of what SS told the company, they can (and perhaps are planning to ) call him as a witness. He can then testify directly to what he himself said and what DM may have said to him.
Here's an explanation of Canadian laws with regard to hearsay evidence:
http://www.duhaime.org/LegalDictionary/H/Hearsay.aspx